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Date: Wed, 28 Feb 2024 19:06:24 -0800
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Subject: Re: [PATCH net-next v2] net: Modify mono_delivery_time with
 clockid_delivery_time
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To: Willem de Bruijn <willemdebruijn.kernel@gmail.com>,
 Abhishek Chauhan <quic_abchauha@quicinc.com>
Cc: kernel@quicinc.com, "David S. Miller" <davem@davemloft.net>,
 Eric Dumazet <edumazet@google.com>, Jakub Kicinski <kuba@kernel.org>,
 Paolo Abeni <pabeni@redhat.com>, netdev@vger.kernel.org,
 linux-kernel@vger.kernel.org, Andrew Halaney <ahalaney@redhat.com>,
 Martin KaFai Lau <martin.lau@kernel.org>
References: <20240228011219.1119105-1-quic_abchauha@quicinc.com>
 <65df56f6ba002_7162829435@willemb.c.googlers.com.notmuch>
From: Martin KaFai Lau <martin.lau@linux.dev>
In-Reply-To: <65df56f6ba002_7162829435@willemb.c.googlers.com.notmuch>
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On 2/28/24 7:53 AM, Willem de Bruijn wrote:
> Sidenote: with sk_clockid, FQ could detect when skb->tstamp is not
> set in monotonic (i.e., set by SO_TXTIME) and drop the packet or
> ignore the embedded timestamp, warn, etc.

Thanks for cc-ing me. Sorry for the late reply. I just catch up to this thread 
and the v1.

I think it is needed to detect if skb->tstamp is monotonic or not in fq. The 
container (with the veth setup) may use sch_etf while the host usually uses fq 
at the physical NIC and expects monotonic skb->tstamp.

During forward (e.g. by bpf_redirect / ip[6]_forward from a veth to a physical 
NIC), skb_clear_tstamp() only forwards the monotonic skb->tstamp now. While 
sch_etf does check sk_clockid first before using skb->tstamp, fq does not check 
that now.
or fq_packet_beyond_horizon() is enough to catch this clock discrepancy?